FIG. 1 depicts a structure of a conventional optical lens assembly. As shown, the conventional optical lens assembly 1 is composed of three pieces of conventional imaging lens 10, 20, 30, a cover glass 80, an image sensor 90 and an IR filter 100. Each imaging lens 10, 20, 30 has two surfaces 11, 12, 21, 22, 31, 32, wherein each surface 11, 21, 31 facing the object side will be referred to as an “object-side surface” and wherein each surface 12, 22, 32 facing the image side will be referred to as an “image-side surface”. The imaging lenses 10, 20, 30 are positioned in a lens base (not shown) through a lens barrel (not shown). A focusing module (not shown) on the lens base drives the lens barrel and changes the relative position and distance between the lens barrel and the image sensor 90 to focus incident light, and to enable the image sensor 90 to sense a clear image. The cover glass 80 protects the image sensor 90. To enable a better sensing of the image, prior to the incident light reaching the image sensor 90, the IR filter 100 is provided to block the IR band wavelengths of the incident light from reaching the image sensor 90, which effectively prevents the image quality from being affected by the IR band rays.
FIGS. 2 to 7 illustrate the spectrum resulting from the IR light filtering effect of conventional IR filters. The conventional imaging lenses used herein are made of E48R material provided by ZEONEX having refractive index of 1.533. Additionally, the IR filter used here are made of glass having on its object-side surface 60 layers of IR filtering thin films, and on its image-side surface 4 layers of anti-reflection layers which have higher transparency to visible light. Please refer to Tables 1-3 for the detail thickness and total thickness of each layer of IR filtering thin films or anti-reflection thin films on the object-side surface and/or the image-side surface of the IR filter:
TABLE 1The object-Total amount of the IR60side surfacefiltering thin filmsMaterialTi3O5SiO2Physical total thickness3377.955331.76(nm)Total thickness (nm)8709.71 nmThe image-Total amount of the4side surfaceanti-reflection thinfilmsMaterialTi3O5SiO2Physical total thickness143.69127.7(nm)Total thickness (nm) 271.39 nm
TABLE 2The object-side surface (IR filtering thin films)Layer12345678910MaterialTi3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Physical116.41185.05113.71178.96106.94171.36108.2173.86105.72171.09thicknessLayer11121314151617181920MaterialTi3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Physical172.32172.46105.42171.28106.98171.74105.41171.73106.8171.45thicknessLayer21222324252627282930MaterialTi3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Physical105.72172.27106.86171.73106.47173.26107.59173.45108.25176.26thicknessLayer31323334353637383940MaterialTi3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Physical110.33178.91113.14183.91115.98186.43116.22184.15114.08181.73thicknessLayer41424344454647484950MaterialTi3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Physical112.9181.36113.72183.6116.38188.88119.59192.59121.6193.77thicknessLayer51525354555657585960MaterialTi3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Ti3O5SiO2Physical122.36194.96122.55195.51121.87193.25193.25120.78118.6195.22thickness
TABLE 3Layer1234The image-MaterialTi3O5SiO2Ti3O5SiO2side surfacephysical17.4830.82126.2296.88(anti-reflectionthicknessthin films)
FIG. 2 shows the spectrum after one piece of the IR filter formed only with the 60 layers of IR filtering thin film on the object-side surface. FIG. 3 shows the spectrum after one piece of the IR filter formed only with the 4 layers of anti-reflection thin film on the image-side surface. FIG. 4 shows a comparison of the spectrums of one piece of the IR filter formed only with 60 layers of IR filtering thin film on the object-side surface, one piece of the IR filter formed only with the 4 layers of anti-reflection thin film on the image-side surface, and one piece of the IR filter formed with the 60 layers of IR filtering thin film on the object-side surface and the 4 layers of anti-reflection thin film on the image-side surface. FIG. 5 shows an enlarged drawing of FIG. 4 in the wavelength range between 850 nm to 1300 nm. The thin line 101 represents the spectrum after one piece of the IR filter formed only with 60 layers of the IR filtering thin film on the object-side surface, the thin line 102 represent the spectrum after one piece of the IR filter formed only with the 4 layers of anti-reflection thin film on the image-side surface, and the bold line 103 represents the spectrum after one piece of the IR filter formed with the 60 layers of IR filtering thin film on the object-side surface and the 4 layers of anti-reflection thin film on the image-side surface. As shown, the IR filter formed with the 60 layers of IR filtering thin film on the object-side surface and the 4 layers of anti-reflection thin film on the image-side surface shows better IR filtering result and transparency to visible light, as compared with the other IR filters.
Tables 4-6 depicts a summary of values of transmittance in the wavelength range between 850 nm to 1300 nm for an IR filter formed with the 60 layers of IR filtering thin film on the object-side surface and the 4 layers of anti-reflection thin film on the image-side surface:
TABLE 4Wavelength (nm)850875900925950975Transmittance (%)65.5963550.1737580.0082520.0000300.0000020.000001
TABLE 5Wavelength (nm)100010251050107511001125Transmittance (%)0.0000010.0000010.0000010.0000010.0000010.000001
TABLE 6Wavelength (nm)1150117512001225125012751300Transmittance (%)0.0003580.0011060.1670900.0940312.99159724.5159004.239430
The transmittance is approximately less than 3% in the range of wavelength between 875 nm to 1250 nm.
The spectrum shown in FIGS. 6 to 7 are obtained based on the transmittance of five pieces of the conventional imaging lens. FIG. 6 shows the spectrum after the conventional optical lens assembly composed of the aforesaid conventional five pieces of the imaging lens and/or one piece of the IR filter, and FIG. 7 shows an enlarged drawing of FIG. 6 in the wavelength range between 850 nm to 1300 nm. The imaging lenses used here are formed with 4 layers of anti-reflection layers on both object-side and image-side surfaces. Please refer to the below Table 7 for the details:
TABLE 7Layer1234The object-MaterialTi3O5SiO2Ti3O5SiO2side surfacePhysical thickness17.4830.82126.2296.88(nm)The image-MaterialTi3O5SiO2Ti3O5SiO2side surfacePhysical thickness17.4830.82126.2296.88(nm)
As illustrated in FIGS. 6 and 7, thin line 111 represents the spectrum only after five pieces of the traditional imaging lens, thin line 112 represents the spectrum only after one piece of the IR filter formed with the 60 layers of IR filtering thin film on the object-side surface and the 4 layers of anti-reflection thin film on the image-side surface, and bold line 113 represents the spectrum after five pieces of the traditional imaging lens and one piece of the IR filter formed with the 60 layers of IR filtering thin film on the object-side surface and the 4 layers of anti-reflection thin film on the image-side surface. As shown, it is clear that even using the IR filter, i.e. the spectrums of the thin line 112 and the bold line 113, the ripple is inevitable. Please refer to the below Tables 8-10 for the details:
TABLE 8Wavelength (nm)850875900925950975Transmittance (%)54.6025130.1362660.0060650.0000210.0000010.000001
TABLE 9Wavelength (nm)100010251050107511001125Transmittance (%)0.0000010.0000010.0000010.0000010.0000010.000001
TABLE 10Wavelength (nm)1150117512001225125012751300Transmittance (%)0.0001420.0004210.0611050.0331381.0217186.3894312.364835
Therefore, the transmittance in the IR light band of one piece of the IR filter formed with 60 layers of IR filtering thin film on the object-side surface and 4 layers of anti-reflection thin film on the image-side surface is approximately less than 3%, and the transmittance for visible light, such as incident light having wavelength between 450 nm to 650 nm, is greater than 80%. With the help of the IR filter formed with the 60 layers of IR filtering thin film on the object-side surface and the 4 layers of anti-reflection thin film on the image-side surface, the transmittance of the optical lens assembly for the IR light band is less than 1.1% and the transmittance for visible light is also very good. However, because the additional IR filter effectively increases the total length of the optical lens assembly, applications of the optical lens assembly in products seeking lighter and thinner appearances are substantially limited.